EP0700709B1 - Process and device for producing a gas using a cascade of membranes working at different temperatures - Google Patents

Process and device for producing a gas using a cascade of membranes working at different temperatures Download PDF

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Publication number
EP0700709B1
EP0700709B1 EP95401914A EP95401914A EP0700709B1 EP 0700709 B1 EP0700709 B1 EP 0700709B1 EP 95401914 A EP95401914 A EP 95401914A EP 95401914 A EP95401914 A EP 95401914A EP 0700709 B1 EP0700709 B1 EP 0700709B1
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Prior art keywords
separator
gas
mixture
waste
permeate
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German (de)
French (fr)
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EP0700709A1 (en
Inventor
Antoine Willemot
Jean-Louis Gelot
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LAir Liquide SA pour lEtude et lExploitation des Procedes Georges Claude
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Air Liquide SA
LAir Liquide SA pour lEtude et lExploitation des Procedes Georges Claude
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    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
    • C01B3/00—Hydrogen; Gaseous mixtures containing hydrogen; Separation of hydrogen from mixtures containing it; Purification of hydrogen
    • C01B3/50—Separation of hydrogen or hydrogen containing gases from gaseous mixtures, e.g. purification
    • C01B3/501—Separation of hydrogen or hydrogen containing gases from gaseous mixtures, e.g. purification by diffusion
    • C01B3/503—Separation of hydrogen or hydrogen containing gases from gaseous mixtures, e.g. purification by diffusion characterised by the membrane
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D53/00—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols
    • B01D53/22—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols by diffusion
    • B01D53/225—Multiple stage diffusion
    • B01D53/226—Multiple stage diffusion in serial connexion
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
    • C01B21/00—Nitrogen; Compounds thereof
    • C01B21/04—Purification or separation of nitrogen
    • C01B21/0405—Purification or separation processes
    • C01B21/0433—Physical processing only
    • C01B21/0438—Physical processing only by making use of membranes
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
    • C01B3/00—Hydrogen; Gaseous mixtures containing hydrogen; Separation of hydrogen from mixtures containing it; Purification of hydrogen
    • C01B3/50—Separation of hydrogen or hydrogen containing gases from gaseous mixtures, e.g. purification
    • C01B3/501—Separation of hydrogen or hydrogen containing gases from gaseous mixtures, e.g. purification by diffusion
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D2257/00—Components to be removed
    • B01D2257/10—Single element gases other than halogens
    • B01D2257/108—Hydrogen
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
    • C01B2203/00—Integrated processes for the production of hydrogen or synthesis gas
    • C01B2203/04—Integrated processes for the production of hydrogen or synthesis gas containing a purification step for the hydrogen or the synthesis gas
    • C01B2203/0405—Purification by membrane separation
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
    • C01B2203/00—Integrated processes for the production of hydrogen or synthesis gas
    • C01B2203/04—Integrated processes for the production of hydrogen or synthesis gas containing a purification step for the hydrogen or the synthesis gas
    • C01B2203/0465—Composition of the impurity
    • C01B2203/047—Composition of the impurity the impurity being carbon monoxide
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
    • C01B2203/00—Integrated processes for the production of hydrogen or synthesis gas
    • C01B2203/04—Integrated processes for the production of hydrogen or synthesis gas containing a purification step for the hydrogen or the synthesis gas
    • C01B2203/0465—Composition of the impurity
    • C01B2203/048—Composition of the impurity the impurity being an organic compound

Definitions

  • the invention relates to the production or separation of gases by membranes according to claim 1 and an installation according to claim 10.
  • the invention is particularly applicable to cases where it is necessary to produce a gas, for example nitrogen, of high purity.
  • the principle is that, under the effect of a partial pressure difference on the part and on the other side of the membrane, we obtain, on the permeate side, a mixture at low pressure, enriched in the most permeable components and at the membrane exit (also called side “residue” or “reject” side), a mixture at a pressure close to the pressure feed (of the incoming mixture) and which is enriched with the least components permeable.
  • operating temperature of the membrane or of the membrane module most often means the temperature obtained inside the membrane or of the module due to the temperature of the incoming gas which passes through it, sometimes with the additional intervention of an external heating system for the membrane module or for maintaining the temperature (thermostatically controlled enclosure).
  • the Yield of the membrane represents the proportion of nitrogen present in the incoming mixture which is found at the outlet (waste) of the membrane
  • EP-A-0 586 018 describes a separation process membrane of a gas, where after passing through a first separator, removing water, and refrigeration with liquid nitrogen, the gas is passed through several membrane separators.
  • an objective of the present invention is to propose a method improved production of a gas, in particular nitrogen, by membrane route.
  • the Applicant has highlighted the fact that it is possible to improve the existing production processes, using at least two separators successive membranes, the operating temperature of the second stage being significantly lower than that of the first membrane stage encountered by the incoming mixture, and the second stage permeate being recycled to the inlet from the first floor.
  • this configuration offers improved performance compared to the permeate scanning technique.
  • the process according to the invention for the production by membrane of a gas high purity from an incoming mixture, whereby the mixture is passed entering a first membrane separator operating at a first operating temperature and passing all or part of the residual mixture from this first membrane separator in a second membrane separator operating at a second operating temperature, the mixture obtained on the permeate side of the second separator being recycled at the inlet of the first separator, is characterized in that the first operating temperature is at least 40 ° C higher than the second Operating temperature.
  • membrane separator is meant according to the invention, a membrane or semi-permeable membrane module, if necessary a set of several semi-permeable membranes (or membrane modules) mounted in parallel, having properties of separation of the gas which one wishes to extract compared to the mixture entering the separator.
  • operating temperature means the notion recalled earlier in this application.
  • the incoming mixture is air and the nitrogen concentration of the gas mixture obtained on the waste side of the second separator membrane is greater than 99% by volume, preferably greater than 99.5 % by volume, and more preferably greater than 99.9% by volume.
  • the membranes used in second separation stage are of a different type from that of the membranes used works in first stage of separation.
  • the membranes used second stage works are of the same type as that of the membranes used first floor.
  • the method according to the invention therefore provides for carrying out substantial cooling. of the residual mixture from the first separation stage, before arriving on the second separation stage.
  • Such a cooling operation could then for example be carried out by conventional means such as mechanical cold, exchanger on cryogenic liquid, or still expansion operation on a turbine.
  • Such a method of cooling by injection of water spray if it has already been mentioned for cooling compressed air at the compressor outlet (as described in document EP-A-524435) in the present case represents cooperation completely attractive and efficient between the phenomenon of water evaporation, energy consumer, and the multi-stage membrane separation producing a very dry second stage permeate, offering significant room for maneuver before to reach water saturation.
  • the incoming mixture before arriving on the first separation stage, undergoes a classic operation for this area of membrane separation, conditioning, allowing operations such as oil removal, filtering, drying or possibly bringing the mixture to temperature.
  • the separator 2 gives rise to the production of a gas mixture on the permeate side 4, and residual side of a gas mixture 5, directed, in the case shown, in its entirety towards the entrance of the second separator 3, which in turn gives rise to the production side permeate of a gas mixture 6, and residual side of a gas mixture 7.
  • the gas mixture 6 is recycled to the inlet of the first stage 2.
  • the two separators membranes 2 and 3 may be of different type or of the same type.
  • FIG. 2 illustrates the case of an installation suitable for implementing the process according to the invention, in the case where it is sought to produce a gaseous mixture 7 high nitrogen purity, from an incoming mixture 1 which is air.
  • Both separators 2 and 3 are then, for the example shown, of the same type, for example of polyimide type, the operating temperature of the separator 2 being largely greater than that of the second separator 3.
  • the air compressor and the stage of conditioning the incoming gas before it arrival on the first floor has not been shown in figure 2.
  • the gas mixture 6 obtained on the permeate side of the second separator is recycled to the inlet of the separator 2, preferably upstream of the air compressor.
  • FIG. 3 illustrates an installation where cooling by means of water injection: we then recognize in Figure 3 the exchanger 8, two-way, one for the residual 5, the other for the permeate 6 into which was injected, before its arrival in the water heat exchanger 10.
  • the water injected into the very dry permeate from the separator 3 will then evaporate, in whole or in part (evaporation can if necessary continue in the exchanger), giving rise to the cooling of the permeate 6, which then exchanges its frigories in exchanger 8 before being recycled at the entrance of the first floor.
  • Figures 4 and 5 illustrate two state-of-the-art installations in the field of membrane production of nitrogen from air, corresponding to the use of two identical separation stages 2 and 3, with respectively in the first case, a recycling of the permeate 6 from the second stage 3 to the entrance of the first stage 2, and in the second case, a scan of the permeate 4 of the first stage 2 using the permeate 6 of the second floor 3.
  • Table I brings together the results of three examples (1A, 1B, 1C) of implementation of a double separation stage, using polyimide type membranes, the second column of the table presenting a comparative example where a single stage separation is used. It will be noted that for each of the three examples according to the invention, using recycling of the permeate at the entrance to the first stage, the "flow rate to be compressed" represents the total air + recycled permeate.
  • example N ° 1A offers, for a comparable membrane surface, a flow saving at compress by almost 30%
  • example N ° 1B offers for an increase membrane surface area of barely 10% (which contributes little to the cost overall investment in the installation) a saving in throughput to be compressed by more than 35%.
  • Example 1C confirms this trend with a gain in compression of more than 40%.
  • Table II presents the results obtained in the case of two state-of-the-art installations (FIGS. 5 and 6), still relative to the same base 100 of the single stage at 45 ° C:
  • Tables III and IV (comparative examples 3A and 3B which are part of the state of the art, and examples 4A and 4B according to the invention) present the same type of comparative study as that presented for tables I and II, but with this time the production of a flow rate of 100 Nm 3 / h of nitrogen containing a residual oxygen concentration of 0.5 vol%, from an incoming mixture of air.
  • Table V presents a variant of the results previously discussed in the context of Examples 1A to 1C (Table I) but where this time, the temperature difference between the two stages is only 20 ° C (Examples 5A and 5B).
  • 100 Nm 3 / h of nitrogen at 0.1% O 2 Comparative example 1 stage T 45 ° C
  • T2 25 ° C
  • T2 25 ° C
  • Membrane surface 100 93 98 Flow to compress 100 76 70

Description

L'invention concerne la production ou séparation de gaz par membranes selon la revendication 1 et une installation selon la revendication 10. L'invention s'applique tout particulièrement aux cas où il est nécessaire de produire un gaz, par exemple de l'azote, de haute pureté.The invention relates to the production or separation of gases by membranes according to claim 1 and an installation according to claim 10. The invention is particularly applicable to cases where it is necessary to produce a gas, for example nitrogen, of high purity.

La production de gaz (notamment l'azote) par des membranes s'est considérablement développée ces dernières années, partout dans le monde, en complément de la production traditionnelle par voie cryogenique, car elle présente les avantages suivants :

  • Une excellente sécurité d'approvisionnement;
  • De faibles coûts de production;
  • La possibilité de fournir, à des coûts très attractifs, selon les applications considérées, des gaz de pureté adaptée.
The production of gases (in particular nitrogen) by membranes has developed considerably in recent years, all over the world, in addition to traditional production by cryogenic means, because it has the following advantages:
  • Excellent security of supply;
  • Low production costs;
  • The possibility of supplying gases of suitable purity at very attractive costs, depending on the applications considered.

Le principe est que, sous l'effet d'une différence de pression partielle de part et d'autre de la membrane, on obtient, côté perméat, un mélange à basse pression, enrichi en composants les plus perméables et en sortie de membrane (aussi appelée côté "résidu" ou coté "rejet"), un mélange à une pression proche de la pression d'alimentation (du mélange entrant) et qui est enrichi en composants les moins perméables.The principle is that, under the effect of a partial pressure difference on the part and on the other side of the membrane, we obtain, on the permeate side, a mixture at low pressure, enriched in the most permeable components and at the membrane exit (also called side "residue" or "reject" side), a mixture at a pressure close to the pressure feed (of the incoming mixture) and which is enriched with the least components permeable.

On utilise ainsi pour produire de l'azote (souvent qualifié de "impur") à partir d'air, des membranes semi-perméables présentant de bonnes propriétés de séparation de l'oxygène par rapport à l'azote (sélectivité), par exemple du type polyimide, le mélange enrichi en oxygène étant obtenu côté perméat. Ces membranes sont souvent qualifiées de membranes "azote".We thus use to produce nitrogen (often qualified as "impure") from air, semi-permeable membranes with good separation properties oxygen with respect to nitrogen (selectivity), for example of the polyimide type, the mixture enriched in oxygen being obtained on the permeate side. These membranes are often qualified as "nitrogen" membranes.

Pour ce qui est de la production d'hydrogène ou de CO, on procède le plus souvent à une récupération à partir de mélanges issus de certaines industries, que l'on sépare sur des membranes semi-perméables présentant de bonnes propriétés de séparation de l'hydrogène par rapport aux autres composants du mélange, par exemple du type polyaramide, le mélange enrichi en hydrogène étant obtenu côté perméat, le mélange enrichi selon les cas en hydrocarbures ou en CO étant obtenu du coté résiduaire de la membrane. Ces membranes sont souvent qualifiées de membranes "hydrogène".As far as hydrogen or CO production is concerned, the most often recovery from mixtures from certain industries, which we separates on semi-permeable membranes having good properties of separation of hydrogen from other components of the mixture, for example of the polyaramide type, the mixture enriched in hydrogen being obtained on the permeate side, the mixture enriched as appropriate with hydrocarbons or CO being obtained from the side residual membrane. These membranes are often called membranes "hydrogen".

Il apparait que les performances obtenues dépendront très largement des conditions d'utilisation de la membrane, telles que la température, la pression d'alimentation de la membrane, ou encore la teneur du mélange entrant en le composant que l'on souhaite extraire côté perméat.It appears that the performances obtained will largely depend on the conditions of use of the membrane, such as temperature, pressure the membrane, or the content of the mixture entering it component that we want to extract on the permeate side.

On sait ainsi pour ce qui est de la température, qu'en augmentant la température de fonctionnement de la membrane, le plus souvent, la perméabilité et donc la productivité de la membrane augmentent, mais sa sélectivité (par exemple O2/N2) et donc le rendement se dégradent. On entend le plus souvent par l'expression "température de fonctionnement de la membrane ou du module membranaire" la température obtenue à l'intérieur de la membrane ou du module du fait de la température du gaz entrant qui y transite, avec parfois l'intervention supplémentaire d'un système extérieur de chauffe du module membranaire ou de maintien en température (enceinte thermostatée).It is thus known with regard to temperature, that by increasing the operating temperature of the membrane, more often than not, the permeability and therefore the productivity of the membrane increase, but its selectivity (for example O 2 / N 2 ) and therefore the yield degrades. The expression "operating temperature of the membrane or of the membrane module" most often means the temperature obtained inside the membrane or of the module due to the temperature of the incoming gas which passes through it, sometimes with the additional intervention of an external heating system for the membrane module or for maintaining the temperature (thermostatically controlled enclosure).

Ainsi, selon les cas, pour obtenir le niveau de performances requises, on chauffera le gaz entrant à plusieurs dizaines de degré, ou on maintiendra ce gaz à la température ambiante, ou encore dans certains cas on refroidira ce gaz en dessous de la température ambiante, voire en dessous de 0°C.Thus, depending on the case, to obtain the required level of performance, we will heat the incoming gas to several tens of degrees, or maintain this gas at the room temperature, or in some cases we will cool this gas below the room temperature or even below 0 ° C.

On rappelera ici, pour le cas de la production d'azote à partir d'air que le "rendement" de la membrane représente la proportion d'azote présente dans le mélange entrant que l'on retrouve à la sortie (résiduaire) de la membrane, la sélectivité O2/N2 de la membrane représente quant à elle le rapport des perméances (on utilise aussi souvent le terme perméabilités) de l'oxygène et de l'azote au travers de la membrane (sel. = Perm (O2) / Perm (N2)).It will be recalled here, for the case of the production of nitrogen from air, that the "yield" of the membrane represents the proportion of nitrogen present in the incoming mixture which is found at the outlet (waste) of the membrane, the O 2 / N 2 selectivity of the membrane represents the ratio of permeances (the term permeabilities is also often used) of oxygen and nitrogen through the membrane (salt. = Perm (O 2 ) / Perm (N 2 )).

En considérant l'exemple de l'azote, des difficultés sont rencontrées lorsqu'il s'agit de produire de l'azote de haute pureté à fort débit (par exemple moins de 0,1 % d'impuretés résiduelles), tout en étant compétitif vis à vis de la voie de production cryogénique ou de la voie de production par adsorption préférentielle;Considering the example of nitrogen, difficulties are encountered when it comes to produce high purity nitrogen at high flow rates (e.g. less than 0.1% residual impurities), while being competitive with the production route cryogenic or preferential adsorption production route;

Il a été proposé (voir notamment les documents US-A-4 894 068, US-A-4 119 417, ou encore EP-A-521 784) de procéder à la séparation selon des installations multi-étagées, qui permettent une réduction de l'investissement et de l'énergie mise en oeuvre, par rapport à un procédé en un seul étage. Ces documents prévoient qu'il est alors avantageux d'effectuer un recyclage des perméats (ou des résiduaires selon le gaz recherché) aval vers les entrées des membranes placées en amont, ou encore le balayage du perméat d'un étage amont par le perméat d'un étage aval.It has been proposed (see in particular documents US-A-4,894,068, US-A-4,119 417, or EP-A-521 784) to separate according to installations multi-stage, which allow a reduction in investment and energy work, compared to a single-stage process. These documents provide that it is then advantageous to recycle permeates (or waste depending on the gas downstream to the inlets of the membranes placed upstream, or the permeate of an upstream stage by permeate of a downstream stage.

Les travaux effectués par la Demanderesse sur ce sujet, tels que notamment rapportés dans le document EP-A-521 784, ont dans un premier temps démontré qu'il était avantageux de procéder à une séparation sur un double étage de séparation, le premier étage de séparation présentant des performances moindres de celles du second étage, par exemple en faisant fonctionner le premier étage à une température supérieure à celle du second étage, ceci en combinaison avec un balayage du perméat du premier étage à l'aide du perméat du second étage.The work carried out by the Applicant on this subject, such as in particular reported in document EP-A-521 784, first demonstrated that was advantageous to carry out a separation on a double separation stage, the first separation stage with lower performance than the second stage, for example by operating the first stage at a temperature higher than that of the second stage, this in combination with a permeate sweep from the first floor using the permeate from the second floor.

Les travaux qu'a poursuivis la Demanderesse montrent que ces solutions, si elles représentent a priori un progrès vis à vis des classiques procédés à un étage, ne sont pas encore suffisamment compétitives, notamment en terme de coût de fonctionnement, pour les cas où il faut dimensionner des unités de grandes taille, pour lesquelles alors ces solutions ne peuvent rivaliser avec l'autre catégorie de production de gaz sur site qui est la production par adsorption préférentielle (PSA).The work carried out by the Applicant shows that these solutions, if they a priori represent progress with respect to conventional one-stage processes, are not not yet sufficiently competitive, particularly in terms of cost of operation, for cases where it is necessary to size large units, for which then these solutions can not compete with the other category of production gas on site which is production by preferential adsorption (PSA).

Le document EP-A-0 586 018 décrit un procédé de séparation membranaire d'un gaz, où après passage dans un premier séparateur, éliminant l'eau, et réfrigération avec de l'azote liquide, le gaz est passé dans plusieurs séparateurs membranaires.EP-A-0 586 018 describes a separation process membrane of a gas, where after passing through a first separator, removing water, and refrigeration with liquid nitrogen, the gas is passed through several membrane separators.

Dans ce contexte, un objectif de la présente invention est de proposer un procédé amélioré de production d'un gaz, notamment d'azote, par voie membranaire.In this context, an objective of the present invention is to propose a method improved production of a gas, in particular nitrogen, by membrane route.

La Demanderesse a mis en évidence le fait qu'il est possible d'améliorer les procédés de production existants, par la mise en oeuvre d'au moins deux séparateurs membranaires successifs, la température de fonctionnement du second étage étant largement inférieure à celle de fonctionnement du premier étage membranaire rencontré par le mélange entrant, et le perméat du second étage étant recyclé à l'entrée du premier étage.The Applicant has highlighted the fact that it is possible to improve the existing production processes, using at least two separators successive membranes, the operating temperature of the second stage being significantly lower than that of the first membrane stage encountered by the incoming mixture, and the second stage permeate being recycled to the inlet from the first floor.

Comme developpé ci-dessous dans le cadre d'exemples, cette configuration offre des performances améliorées par rapport à la technique du balayage des perméats.As developed below in the context of examples, this configuration offers improved performance compared to the permeate scanning technique.

D'autre part, le recyclage du second perméat "froid" à l'entrée du premier étage permet de réduire la quantité d'énergie nécessaire pour comprimer le mélange entrant, donc le dimensionnement du compresseur de gaz. On obtient donc de façon paradoxale et avantageuse une réduction possible de l'investissement tout en améliorant la sélectivité du système.On the other hand, the recycling of the second "cold" permeate at the entrance of the first floor reduces the amount of energy required to compress the incoming mixture, therefore the sizing of the gas compressor. So we get paradoxically and advantageous a possible reduction in investment while improving the system selectivity.

Ainsi, le procédé selon l'invention, de production par voie membranaire d'un gaz de haute pureté à partir d'un mélange entrant, selon lequel on fait passer le mélange entrant dans un premier séparateur membranaire fonctionnant à une première température de fonctionnement et l'on fait passer tout ou partie du mélange résiduaire issu de ce premier séparateur membranaire dans un second séparateur membranaire fonctionnant à une seconde température de fonctionnement, le mélange obtenu coté perméat du second séparateur étant recyclé à l'entrée du premier séparateur, se caractérise en ce que la première température de fonctionnement est supérieure d'au moins 40°C à la seconde température de fonctionnement.Thus, the process according to the invention, for the production by membrane of a gas high purity from an incoming mixture, whereby the mixture is passed entering a first membrane separator operating at a first operating temperature and passing all or part of the residual mixture from this first membrane separator in a second membrane separator operating at a second operating temperature, the mixture obtained on the permeate side of the second separator being recycled at the inlet of the first separator, is characterized in that the first operating temperature is at least 40 ° C higher than the second Operating temperature.

Par "séparateur membranaire", on entend selon l'invention, une membrane ou module membranaire semi-perméable, le cas échéant un ensemble de plusieurs membranes (ou modules membranaires) semi-perméables montées en parallèle, présentant des propriétés de séparation du gaz que l'on souhaite extraire par rapport au mélange entrant dans le séparateur.By "membrane separator" is meant according to the invention, a membrane or semi-permeable membrane module, if necessary a set of several semi-permeable membranes (or membrane modules) mounted in parallel, having properties of separation of the gas which one wishes to extract compared to the mixture entering the separator.

Ainsi, à titre d'exemple, on pourra utiliser, pour produire de l'azote de haute pureté à partir d'un mélange entrant qui est de l'air, des modules membranaires de type polyimide ou encore de type polyaramide.So, for example, we can use, to produce high nitrogen purity from an incoming mixture which is air, type membrane modules polyimide or polyaramide type.

On entend par "température de fonctionnement" selon l'invention, la notion rappelée plus haut dans la présente demande. The term "operating temperature" according to the invention means the notion recalled earlier in this application.

Selon une des mises en oeuvre de l'invention, le mélange entrant est de l'air et la concentration en azote du mélange gazeux obtenu coté résiduaire du second séparateur membranaire est supérieure à 99% volumiques, préférentiellement supérieure à 99,5 % volumiques, et plus préférentiellement supérieure à 99,9% volumiques.According to one of the embodiments of the invention, the incoming mixture is air and the nitrogen concentration of the gas mixture obtained on the waste side of the second separator membrane is greater than 99% by volume, preferably greater than 99.5 % by volume, and more preferably greater than 99.9% by volume.

Selon une des mises en oeuvre de l'invention, les membranes mises en oeuvre en second étage de séparation sont de type différent de celui des membranes mises en oeuvre en premier étage de séparation.According to one of the embodiments of the invention, the membranes used in second separation stage are of a different type from that of the membranes used works in first stage of separation.

Selon une autre des mises en oeuvre de l'invention, les membranes mises en oeuvre en second étage sont de même type que celui des membranes mises en oeuvre en premier étage.According to another of the implementations of the invention, the membranes used second stage works are of the same type as that of the membranes used first floor.

Le procédé selon l'invention prévoit donc d'effectuer un refroidissement sensible du mélange résiduaire issu du premier étage de séparation, avant son arrivée sur le second étage de séparation.The method according to the invention therefore provides for carrying out substantial cooling. of the residual mixture from the first separation stage, before arriving on the second separation stage.

Il est à noter que ce refroidissement important peut être envisagé en toute sécurité dans cette cascade de séparateurs du fait que le gaz issu du premier étage est généralement très sec (point de rosée de -60°C, voire -70°C).It should be noted that this significant cooling can be envisaged in complete safety in this cascade of separators because the gas from the first stage is generally very dry (dew point of -60 ° C, even -70 ° C).

Une telle opération de refroidissement pourra alors par exemple être effectuée par des moyens classiques tels que froid mécanique, échangeur sur liquide cryogénique, ou encore opération de détente sur une turbine.Such a cooling operation could then for example be carried out by conventional means such as mechanical cold, exchanger on cryogenic liquid, or still expansion operation on a turbine.

Mais la Demanderesse a mis en évidence une méthode particulièrement avantageuse pour effectuer cette opération de refroidissement, qui consiste à injecter de l'eau sous forme pulvérisée dans le perméat très sec issu du second étage de séparation, donnant lieu à l'évaporation de tout ou partie de cette eau dans le perméat (du fait de la marge existante par rapport au point de saturation), cette évaporation, endothermique, "pompant" une partie de l'énergie du perméat, ce qui entraíne un abaissement de la température de ce perméat. Ce flux perméat ainsi refroidi est alors envoyé vers un échangeur de gaz comprenant au moins deux voies, où il échange ses frigories avec le résiduaire issu de la première étape de séparation.But the Applicant has highlighted a method particularly advantageous for carrying out this cooling operation, which consists in injecting water in spray form in very dry permeate from the second stage of separation, giving rise to the evaporation of all or part of this water in the permeate (due to the existing margin relative to the saturation point), this evaporation, endothermic, "pumping" part of the energy of the permeate, which results in a lowering the temperature of this permeate. This permeate flow thus cooled is then sent to a gas exchanger comprising at least two channels, where it exchanges its frigories with the residue from the first separation step.

Il est d'ailleurs possible, et avantageux, d'asservir le débit d'injection d'eau dans le second perméat à la température du mélange entrant dans le second séparateur.It is also possible, and advantageous, to control the water injection rate in the second permeate at the temperature of the mixture entering the second separator.

Un tel mode de refroidissement par injection d'eau pulvérisée, s'il a déjà été évoqué pour le refroidissement d'un air comprimé en sortie de compresseur (comme décrit dans le document EP-A-524435) représente dans le cas présent une coopération tout à fait attractive et performante entre le phénomène d'évaporation d'eau, consommateur d'énergie, et le multi-étage de séparation membranaire produisant un perméat de second étage très sec, offrant une marge de manoeuvre importante avant d'atteindre la saturation en eau. Such a method of cooling by injection of water spray, if it has already been mentioned for cooling compressed air at the compressor outlet (as described in document EP-A-524435) in the present case represents cooperation completely attractive and efficient between the phenomenon of water evaporation, energy consumer, and the multi-stage membrane separation producing a very dry second stage permeate, offering significant room for maneuver before to reach water saturation.

Elle apporte avant tout un coût de fonctionnement et d'investissement incomparablement plus faible que celui des méthodes citées plus haut et traditionnellement utilisées dans le milieu de la séparation membranaire, l'eau représentant une source de "froid" comparativement presque gratuite.Above all, it brings an operating and investment cost incomparably weaker than that of the methods mentioned above and traditionally used in the medium of membrane separation, water representing a comparatively almost free source of "cold".

Comme il apparaítra clairement à l'homme du métier, dans tous les cas déjà cités, le mélange entrant, avant son arrivée sur le premier étage de séparation, subit une opération classique pour ce domaine de la séparation membranaire, de conditionnement, permettant de réaliser des opérations telles que déshuilage, filtrage, séchage ou encore mise en température éventuelle du mélange.As will be clear to those skilled in the art, in all the cases already cited, the incoming mixture, before arriving on the first separation stage, undergoes a classic operation for this area of membrane separation, conditioning, allowing operations such as oil removal, filtering, drying or possibly bringing the mixture to temperature.

D'autres caractéristiques et avantages de la présente invention ressortiront de la description suivante de modes de réalisation donnés à titre illustratif mais nullement limitatif, faite en relation avec les dessins annexés, sur lesquels :

  • La figure 1 est une représentation schématique d'une installation bi-étagée convenant pour la mise en oeuvre du procédé selon l'invention.
  • La figure 2 est une représentation schématique d'une installation bi-étagée convenant pour la mise en oeuvre du procédé selon l'invention, en vue d'obtenir à partir d'un mélange entrant d'air, un azote de haute pureté,.
  • La figure 3 est une représentation schématique d'une installation bi-étagée convenant pour la mise en oeuvre du procédé selon l'invention, en vue d'obtenir à partir d'un mélange entrant d'air, un azote de haute pureté, et mettant en oeuvre un refroidissement par injection d'eau dans le perméat issu du second étage de séparation.
  • Les figures 4 et 5 illustrent deux installations de l'état de l'art dans le domaine de la production membranaire d'azote à partir d'air, correspondant à la mise en oeuvre de deux étages de séparation identiques, avec respectivement un recyclage du perméat du second étage vers l'entrée du premier étage, et un balayage du perméat du premier étage à l'aide du perméat du second étage.
Other characteristics and advantages of the present invention will emerge from the following description of embodiments given by way of illustration but in no way limiting, made in relation to the appended drawings, in which:
  • Figure 1 is a schematic representation of a two-stage installation suitable for the implementation of the method according to the invention.
  • FIG. 2 is a schematic representation of a two-stage installation suitable for implementing the method according to the invention, with a view to obtaining, from an incoming air mixture, high purity nitrogen.
  • FIG. 3 is a schematic representation of a two-stage installation suitable for implementing the method according to the invention, with a view to obtaining from an incoming mixture of air, a nitrogen of high purity, and using cooling by injecting water into the permeate from the second separation stage.
  • FIGS. 4 and 5 illustrate two state-of-the-art installations in the field of membrane production of nitrogen from air, corresponding to the use of two identical separation stages, with recycling of the second stage permeate to the first stage entrance, and a sweep of the first stage permeate using the second stage permeate.

On reconnaít sur la figure 1 la présence d'un premier séparateur membranaire 2, alimenté par un mélange entrant 1, l'étape de conditionnement éventuelle du mélange 1 avant son arrivée sur le séparateur 2 n'a pas été représentée.We recognize in Figure 1 the presence of a first membrane separator 2, fed by an incoming mixture 1, the possible conditioning step of the mixture 1 before its arrival on the separator 2 has not been shown.

Le séparateur 2 donne lieu à la production côté perméat d'un mélange gazeux 4, et côté résiduaire d'un mélange gazeux 5, dirigé, dans le cas représenté, dans sa totalité vers l'entrée du second séparateur 3, qui à son tour donne lieu à la production côté perméat d'un mélange gazeux 6, et côté résiduaire d'un mélange gazeux 7.The separator 2 gives rise to the production of a gas mixture on the permeate side 4, and residual side of a gas mixture 5, directed, in the case shown, in its entirety towards the entrance of the second separator 3, which in turn gives rise to the production side permeate of a gas mixture 6, and residual side of a gas mixture 7.

Le mélange gazeux 6 est recyclé à l'entrée du premier étage 2.The gas mixture 6 is recycled to the inlet of the first stage 2.

Comme illustré plus loin dans le cadre d'exemples, les deux séparateurs membranaires 2 et 3 pourront être de type différent ou encore de même type.As illustrated below in the context of examples, the two separators membranes 2 and 3 may be of different type or of the same type.

La figure 2 illustre le cas d'une installation convenant pour la mise en oeuvre du procédé selon l'invention, dans le cas où l'on cherche à produire un mélange gazeux 7 de haute pureté en azote, à partir d'un mélange entrant 1 qui est de l'air. Les deux séparateurs 2 et 3, sont alors, pour l'exemple représenté, de même type, par exemple de type polyimide, la température de fonctionnement du séparateur 2 étant largement supérieure à celle du second séparateur 3.FIG. 2 illustrates the case of an installation suitable for implementing the process according to the invention, in the case where it is sought to produce a gaseous mixture 7 high nitrogen purity, from an incoming mixture 1 which is air. Both separators 2 and 3 are then, for the example shown, of the same type, for example of polyimide type, the operating temperature of the separator 2 being largely greater than that of the second separator 3.

Le compresseur d'air et l'étape de conditionnement du gaz entrant avant son arrivée sur le premier étage (comprenant des étapes telles que séchage, filtrage, déshuilage ou encore mise en température éventuelle du gaz) n'a pas été représentée sur la figure 2.The air compressor and the stage of conditioning the incoming gas before it arrival on the first floor (including stages such as drying, filtering, oil removal or possible gas heating) has not been shown in figure 2.

Le mélange gazeux 6 obtenu coté perméat du second séparateur est recyclé vers l'entrée du séparateur 2, préférentiellement en amont du compresseur d'air.The gas mixture 6 obtained on the permeate side of the second separator is recycled to the inlet of the separator 2, preferably upstream of the air compressor.

On reconnaít sur la figure 2 la présence d'un échangeur de chaleur 8, utilisé pour refroidir le mélange gazeux 5, le mélange gazeux 6, plus froid, libérant ses frigories dans l'échangeur avant son arrivée à l'entrée du séparateur 2. Le mélange gazeux 7 à haute teneur en azote, transite ici par un refroidisseur (par exemple du type cryogénique) avant de libérer ses frigories dans l'échangeur 8, puis son arrivée au poste utilisateur final (poste utilisateur non représenté sur la figure 2).We recognize in Figure 2 the presence of a heat exchanger 8, used for cool the gas mixture 5, the gas mixture 6, colder, releasing its frigories in the exchanger before it arrives at the inlet of the separator 2. The gas mixture 7 to high nitrogen content, transits here through a cooler (for example of the type cryogenic) before releasing its frigories in the exchanger 8, then its arrival at the end user station (user station not shown in Figure 2).

La figure 2 n'illustre qu'une des nombreuses variantes de réalisation de l'opération double de refroidissement du résiduaire issu du premier étage de séparation et de réchauffement et recyclage du perméat de second étage. On pourrait aussi par exemple envisager les solutions suivantes, non représentées mais décrites ici à titre illustratif :

  • l'échangeur 8 n'est qu'à deux voies, une pour le refroidissement du résiduaire 5 et l'autre pour le résiduaire 7 qui y libère ses frigories après passage dans le refroidisseur;
  • une autre solution où le refroidisseur 9 est disposé entre l'échangeur 8 et le séparateur 3, le résiduaire 5 étant donc refroidi, après son passage sur l'échangeur 8, qui est un échangeur trois voies, les deux autres voies étant utilisées pour le recyclage du perméat 6 vers l'entrée du premier étage et pour le résiduaire 7 qui y libère ses frigories avant d'être dirigé vers le poste utilisateur final;
  • une autre solution est une variante de la solution précédente, où le résiduaire 7 ne transite pas par l'échangeur qui est alors un échangeur deux voies;
  • on peut aussi envisager une solution sans échangeur 8, avec la présence d'un simple refroidisseur sur le trajet du résiduaire 5 entre les deux séparateurs 2 et 3, le perméat 6 étant alors recyclé directement vers l'entrée du premier étage, sans étape intermédiaire, de même que le résiduaire 7 est directement dirigé vers le poste utilisateur.
FIG. 2 illustrates only one of the numerous alternative embodiments of the double operation of cooling the waste from the first stage of separation and of heating and recycling of the permeate of the second stage. One could also for example consider the following solutions, not shown but described here by way of illustration:
  • the exchanger 8 is only two-way, one for cooling the waste 5 and the other for the waste 7 which releases its frigories there after passing through the cooler;
  • another solution where the cooler 9 is disposed between the exchanger 8 and the separator 3, the waste 5 being therefore cooled, after passing over the exchanger 8, which is a three-way exchanger, the other two ways being used for the recycling of the permeate 6 to the entrance of the first floor and for the residual 7 which releases its frigories there before being sent to the end user station;
  • another solution is a variant of the previous solution, where the waste 7 does not pass through the exchanger which is then a two-way exchanger;
  • we can also consider a solution without exchanger 8, with the presence of a simple cooler on the path of the waste 5 between the two separators 2 and 3, the permeate 6 then being recycled directly to the entrance of the first floor, without intermediate step , just as the residual 7 is directly directed to the user station.

La figure 3 illustre une installation où est mis en oeuvre un refroidissement par injection d'eau : on reconnaít alors sur la figure 3 l'échangeur 8, à deux voies, une pour le résiduaire 5, l'autre pour le perméat 6 dans lequel a été injectée, avant son arrivée dans l'échangeur de l'eau 10 pulvérisée. L'eau injectée dans le perméat très sec issu du séparateur 3 va alors s'évaporer, en tout ou partie (l'évaporation pouvant le cas échéant se poursuivre dans l'échangeur), donnant lieu au refroidissement du perméat 6, qui échange alors ses frigories dans l'échangeur 8 avant d'être recyclé à l'entrée du premier étage.FIG. 3 illustrates an installation where cooling by means of water injection: we then recognize in Figure 3 the exchanger 8, two-way, one for the residual 5, the other for the permeate 6 into which was injected, before its arrival in the water heat exchanger 10. The water injected into the very dry permeate from the separator 3 will then evaporate, in whole or in part (evaporation can if necessary continue in the exchanger), giving rise to the cooling of the permeate 6, which then exchanges its frigories in exchanger 8 before being recycled at the entrance of the first floor.

Les figures 4 et 5 illustrent deux installations de l'état de l'art dans le domaine de la production membranaire d'azote à partir d'air, correspondant à la mise en oeuvre de deux étages de séparation identiques 2 et 3, avec respectivement dans le premier cas, un recyclage du perméat 6 du second étage 3 vers l'entrée du premier étage 2, et dans le second cas, un balayage du perméat 4 du premier étage 2 à l'aide du perméat 6 du second étage 3.Figures 4 and 5 illustrate two state-of-the-art installations in the field of membrane production of nitrogen from air, corresponding to the use of two identical separation stages 2 and 3, with respectively in the first case, a recycling of the permeate 6 from the second stage 3 to the entrance of the first stage 2, and in the second case, a scan of the permeate 4 of the first stage 2 using the permeate 6 of the second floor 3.

Une installation telle que celle illustrée dans le cadre de la figure 2 a été testée pour la production d'un débit de 100 Nm3/h d'azote contenant une concentration résiduelle d'oxygène de 0,1 % volumiques, à partir d'un mélange entrant d'air.An installation such as that illustrated in the context of FIG. 2 has been tested for the production of a flow rate of 100 Nm 3 / h of nitrogen containing a residual oxygen concentration of 0.1% by volume, starting from an incoming mixture of air.

Le tableau I rassemble les résultats de trois exemples (1A, 1B, 1C) de mise en oeuvre d'un double étage de séparation, mettant en oeuvre des membranes de type polyimide, la seconde colonne du tableau présentant un exemple comparatif où un seul étage de séparation est utilisé. On notera que pour chacun des trois exemples selon l'invention, utilisant un recyclage du perméat à l'entrée du premier étage, le "débit à comprimer" représente le total air + perméat recyclé. Table I brings together the results of three examples (1A, 1B, 1C) of implementation of a double separation stage, using polyimide type membranes, the second column of the table presenting a comparative example where a single stage separation is used. It will be noted that for each of the three examples according to the invention, using recycling of the permeate at the entrance to the first stage, the "flow rate to be compressed" represents the total air + recycled permeate.

exemple comparatif : comparative example :

  • un seul étage de membrane polyimide, température de fonctionnement : 45°C;single stage of polyimide membrane, operating temperature: 45 ° C;
  • surface de membrane mise en oeuvre : 100membrane surface used: 100
exemple N°1A : example N ° 1A :

  • température de fonctionnement du premier étage = 45°C, température de fonctionnement du second étage = 5°C;operating temperature of the first stage = 45 ° C, temperature of second stage operation = 5 ° C;
  • les deux étages mettent en oeuvre la même surface de membrane (Surf1=Surf2)the two stages use the same membrane surface (Surf1 = surf2)
exemple N°1B : example N ° 1B :

  • température de fonctionnement du premier étage = 45°C, température de fonctionnement du second étage = 5°C;operating temperature of the first stage = 45 ° C, temperature of second stage operation = 5 ° C;
  • le second étage met en oeuvre deux fois plus de surface de membrane que le premier étage (Surf2=2 x Surf1)the second stage uses twice as much membrane surface as the first floor (Surf2 = 2 x Surf1)
exemple N°1C : example N ° 1C :

  • température de fonctionnement du premier étage = 45°C, température de fonctionnement du second étage = 5°C; operating temperature of the first stage = 45 ° C, temperature of second stage operation = 5 ° C;
  • le second étage met en oeuvre quatre fois plus de surface de membrane que le premier étage (Surf2=4 x Surf1)the second stage uses four times more membrane surface than the first floor (Surf2 = 4 x Surf1)

On constate alors sur les résultats présentés que par rapport à l'exemple comparatif qui représente une base 100, tant pour la surface de membrane utilisée que pour le débit à comprimer (donc l'énergie de compression mise en oeuvre), l'exemple N° 1A offre, pour une surface de membrane comparable, une économie de débit à comprimer de près de 30%, l'exemple N°1B offre quant à lui pour une augmentation de surface de membrane d'à peine 10 % (ce qui intervient faiblement dans le coût d'investissement global de l'installation) une économie de débit à comprimer de plus de 35 %.We can see from the results presented that compared to the example comparison which represents a base 100, both for the membrane surface used and for the flow to be compressed (therefore the compression energy used), the example N ° 1A offers, for a comparable membrane surface, a flow saving at compress by almost 30%, example N ° 1B offers for an increase membrane surface area of barely 10% (which contributes little to the cost overall investment in the installation) a saving in throughput to be compressed by more than 35%.

L'exemple 1C confirme cette tendance avec un gain sur la compression de plus de 40 %.Example 1C confirms this trend with a gain in compression of more than 40%.

A titre de comparaison, le tableau II présente les résultats obtenus dans le cas de deux installations de l'état de l'art (figures 5 et 6), toujours par rapport à la même base 100 du monoétage à 45°C :By way of comparison, Table II presents the results obtained in the case of two state-of-the-art installations (FIGS. 5 and 6), still relative to the same base 100 of the single stage at 45 ° C:

exemple 2A - comparatif : example 2A - comparative:

  • double étage polyimide, fonctionnant à 45°C, les deux étages mettent en oeuvre la même surface de membrane;polyimide double stage, operating at 45 ° C, the two stages bring works the same membrane surface;
  • recyclage du second perméat à l'entrée du premier étagerecycling of the second permeate at the entrance to the first floor
exemple 2B comparatif :comparative example 2B :

  • double étage polyimide, fonctionnant à 45°C, les deux étages mettent en oeuvre la même surface de membrane;polyimide double stage, operating at 45 ° C, the two stages bring works the same membrane surface;
  • balayage du premier perméat à l'aide du second perméatscanning of the first permeate using the second permeate

On constate à la lecture de ce tableau que l'économie sur la compression est infime, et non compensée par la diminution négligeable de surface de membrane mise en oeuvre, qui comme signalé plus haut intervient, pour de telles proportions, peu dans le coût global d'investissement.We see from reading this table that the economy on compression is tiny, and not compensated for by the negligible reduction in the area of membrane put implemented, which as mentioned above intervenes, for such proportions, little in the overall investment cost.

Les tableaux III et IV (exemples 3A et 3B comparatifs s'inscrivant dans l'état de l'art, et les exemples 4A et 4B selon l'invention) présentent le même type d'étude comparative que celle présentée pour les tableaux I et II, mais avec cette fois la production d'un débit de 100 Nm3/h d'azote contenant une concentration résiduelle d'oxygène de 0,5 % volumiques, à partir d'un mélange entrant d'air. Tables III and IV (comparative examples 3A and 3B which are part of the state of the art, and examples 4A and 4B according to the invention) present the same type of comparative study as that presented for tables I and II, but with this time the production of a flow rate of 100 Nm 3 / h of nitrogen containing a residual oxygen concentration of 0.5 vol%, from an incoming mixture of air.

Ces deux tableaux confirme toutes les conclusions déjà établies dans le cadre de la pureté à 0,1 %.These two tables confirm all the conclusions already established within the framework of 0.1% purity.

Le tableau V présente quant à lui une variante des résultats précédemment discutés dans le cadre des exemples 1A à 1C (tableau I) mais où cette fois, la différence de température entre les deux étages n'est que de 20 °C (exemples 5A et 5B).

Figure 00100001
Figure 00110001
100 Nm3/h d'azote à 0,1 % O2 Exemple comparatif 1 étage T = 45°C Selon l'invention : exemple 5A 2 étages avec recyclage Surf. 2 = Surf. 1 T1 = 45°C ; T2 = 25°C Selon l'invention : exemple 5B 2 étages avec recyclage Surf. 2 = 2 x Surf. 1 T = 45°C ; T2 = 25°C Surface de membrane 100 93 98 Débit à comprimer 100 76 70 Table V presents a variant of the results previously discussed in the context of Examples 1A to 1C (Table I) but where this time, the temperature difference between the two stages is only 20 ° C (Examples 5A and 5B).
Figure 00100001
Figure 00110001
100 Nm 3 / h of nitrogen at 0.1% O 2 Comparative example 1 stage T = 45 ° C According to the invention: example 5A 2 stages with recycling Surf. 2 = Surf. 1 T1 = 45 ° C; T2 = 25 ° C According to the invention: example 5B 2 stages with recycling Surf. 2 = 2 x Surf. 1 T = 45 ° C; T2 = 25 ° C Membrane surface 100 93 98 Flow to compress 100 76 70

Claims (10)

  1. Process for producing a high-purity gas by means of a membrane starting from an incoming gas mixture containing the said gas (1), in which a membrane separation of the said gas is carried out in succession in at least a first membrane separator (2) and a second membrane separator (3) in series, in the following manner: the incoming gas mixture is made to pass through the first separator (2) working at a first working temperature and all or some of the waste gas (5) coming from this first separator is made to pass through the second separator (3) working at a second working temperature, in order to obtain the said production gas as waste output from the second separator, the gas mixture obtained on the permeate side of the second separator being recycled into the inlet of the first separator, characterized in that the first working temperature is at least 40°C above the second working temperature.
  2. Process according to Claim 1, characterized in that membranes of different type are used for the first and second separators.
  3. Process according to Claim 1, characterized in that membranes of the same type are used for the first and second separators.
  4. Process according to one of Claims 1 to 3, characterized in that the waste gas (5) coming from the first separator (2) is brought into heat exchange relationship with at least one cooled gas (6; 7) coming from the second separator (3).
  5. Process according to Claim 4, characterized in that the cooled gas is the gas mixture (6) obtained from the permeate side of the second separator into which gas mixture sprayed water (10) is injected.
  6. Process according to Claim 4, characterized in that the cooled gas is the waste gas (7) from the second separator (3).
  7. Process according to one of Claims 1 to 6, characterized in that the incoming mixture is air.
  8. Process according to Claim 7, characterized in that the production gas is nitrogen.
  9. Process according to Claim 8, characterized in that the nitrogen concentration of the gas mixture obtained on the waste side of the last separator is greater than 99 vol%, preferably greater than 99.5 vol% and even more preferably greater than 99.9 vol%.
  10. Plant for producing high-purity nitrogen by membrane means, in order to feed a user station for implementing the process according to either of Claims 8 and 9, comprising:
    a first membrane separator (2);
    a second membrane separator (3) ;
    a line for recycling the gas mixture obtained as the permeate output from the second separator into the inlet of the first separator;
    a gas-cooling system (9) placed at one of the following locations:
    a) in a line connecting the outlet for the waste (5) from the first separator (2) to the inlet of the second separator (3);
    b) in a line connecting the outlet for the waste (7) from the second separator (3) to the user station;
    c) in the recycling line connecting the outlet for the permeate (6) from the second separator (3) to the inlet of the first separator (2);
    an at least two-way exchanger (8) placed in such a way that:
    in case a), the inlet of a first way of the exchanger is connected to the outlet for the waste (5) from the first separator, the outlet for this first way being connected to the inlet of the cooler (9), the other ways of the exchanger making the permeate mixture (6) from the second separator (3) pass to the inlet of the first separator (2) and/or making the waste mixture (7) coming from the second separator (3) pass to the said user station;
    in case b), the inlet of a first way of the exchanger is connected to the outlet of the cooler system, the outlet of this first way being connected to the said user station, the other ways of the exchanger making the waste mixture (5) coming from the first separator pass between the first separator and the second separator and, where appropriate, making the permeate mixture (6) coming from the second separator (3) pass to the inlet of the first separator (2);
    in case c) , the cooler system includes means for injecting sprayed water into the permeate mixture (6) coming from the second separator (3), the inlet of a first way of the exchanger receiving the permeate mixture into which the sprayed water has been injected, the outlet of this first way being connected to the inlet of the first separator (2), the other ways of the exchanger making the waste mixture (5) coming from the first separator (2) pass between the first separator and the second separator and, where appropriate, making the waste mixture (7) coming from the second separator (3) pass between this second separator and the said user station.
EP95401914A 1994-09-12 1995-08-18 Process and device for producing a gas using a cascade of membranes working at different temperatures Expired - Lifetime EP0700709B1 (en)

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EP95401916A Expired - Lifetime EP0700711B1 (en) 1994-09-12 1995-08-18 Process and device for gas separation using membranes

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FR2724327B1 (en) 1996-10-25
EP0700710B1 (en) 2001-10-17
JPH08196853A (en) 1996-08-06
EP0700711B1 (en) 2000-01-12
CA2158008A1 (en) 1996-03-13
ES2143020T3 (en) 2000-05-01
DE69523244T2 (en) 2002-06-27
EP0700710A1 (en) 1996-03-13
CA2157990A1 (en) 1996-03-13
CN1127672A (en) 1996-07-31
FR2724327A1 (en) 1996-03-15
EP0700709A1 (en) 1996-03-13
DE69514454D1 (en) 2000-02-17
US5538536A (en) 1996-07-23
JPH08198606A (en) 1996-08-06
EP0700711A1 (en) 1996-03-13
CN1128175A (en) 1996-08-07
DE69514454T2 (en) 2000-08-03
JPH08173749A (en) 1996-07-09
CN1130096A (en) 1996-09-04
DE69523244D1 (en) 2001-11-22
DE69525004D1 (en) 2002-02-21
CA2157989A1 (en) 1996-03-13

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